So-called key actuated switches have been known heretofore. For example, R. C. Cressman et al U.S. Pat. No. 2,771,521, dated Nov. 20, 1956, shows a key actuated switch wherein the key is provided with a notch in one edge of its stem adjacent to the handle. This prevents turning of the key if incorrectly inserted into the keyhole and allows use of only a special key to operate the switch. The key is the movable contact of the switch. Also, R. J. Persia et al U.S. Pat. No. 3,321,589, dated May 23, 1967, shows a safety lock switch for a punch press. A safety block is chained to the key and the key is removable from the lock only when the lock switch is "off". Therefore, the safety block can be placed between the dies of the press only when it is "off" for safety. Furthermore, S. W. Grebner U.S. Pat. No. 4,013,858, dated Mar. 22, 1977, assigned to the assignee of this invention, shows a rocker switch with integral off-lock that has a locking mechanism generally similar to that used in the present invention.
While these prior devices have been useful for their intended purposes, this invention relates to improvements thereover.